1. Field of the Invention
This invention relates to a process and apparatus for the manufacture of a permanent, tight pipe joint.
2. Background Information
The generic process for the manufacture of a permanent, tight pipe joint, consisting of a press fitting surrounding at least one smooth-ended pipe end and having a stop on the inside at some distance from the open end, in which first the pipe is inserted axially into the press fitting, and then by means of a pressing tool surrounding the press fitting and having several jaws, the press fitting is pressed to form a positive and non-positive connection with the inserted pipe end, after the application of the pressing tool and the movement of the jaws closer to one another. (See brochure published by Mannesmann Edelstahlrohr GmbH, 1988 Edition). This process, known as the Mannesmann Press Fitting System, has been successfully used for many years in heating and installation technology, and has also been used in other applications. The quality of the pipe joint is essentially a function of the quality of the parts to be connected and of the O-ring used. The quality of the pipe joint is also a function of how closely the assembly instructions are followed. Reference is made to the latter point in the above mentioned brochure, in Chapter 4 (Assembly Instructions), with reference to FIG. 6f. According to these instructions, the pipe must be pushed into the press fitting with a slight rotation and simultaneous pressure in the axial direction, up to the press fitting stop, since an insufficient inserted length can have an adverse effect on the strength of the joint.
The system makes it possible to check the position of the inserted pipe, to the extent that the different shapes of fittings, as mentioned above, have a stop located on the inside at some distance from the open end. The distance of the stop from the open end is thereby selected so that it at least equals the insertion length required to achieve a correct pressing. The stop thus provides resistance against further axial insertion of the pipe and is a signal for the pipe fitter that the pipe has reached the desired insertion position.
In spite of this checking capability, the quality and endurance of the pipe joint at this point, too, are a function of the skill and reliability of the pipe fitter. With regard to an additional checking capability, it has already been proposed that the required insertion length be marked on the end of the pipe, e.g. in the form of a triangle, an arrow, or a similar shape. This proposal has the disadvantage that, depending on the conditions on the assembly site, this marking is not always readily visible, and if the marking is not applied over the entire circumference, it can wind up on the side facing away from the pipe fitter. In any case, a marking on the pipe can also be disregarded, just as the assembly instructions can be disregarded, so that regardless of the presence of any markings, the quality of the joint to be made is still dependent on the reliability and skill of the person making the pipe joint.